A machine tool (e.g., a milling machine, a machining center, etc.) provided with a spindle (a, so-called tool spindle) for fixedly supporting a tool and rotating, is configured such that various cutting operations can be carried out by selecting a suitable tool from among several types of tools respectively fitted to tool holders and attaching it to an axial end of the spindle (hereinafter referred to as a spindle nose) in an exchangeable manner. To this end, generally, a machine tool is provided, inside a spindle head device including a tool spindle, with a tool retaining mechanism for detachably retaining respective tool holders on the spindle nose.
A tool holder is provided with a chuck for chucking a tool, a shank adapted to be received and held in the spindle nose, and a flange adapted to be grasped by an automatic tool changer (ATC) and usually provided between the chuck and the shank. Correspondingly, the spindle nose is provided with a receiving recess for detachably receiving the shank (also referred to as a tool shank) of the tool holder. On the other hand, the tool retaining mechanism includes a movable clamping element for releasably clamping the tool shank and an actuating element for displacing the movable clamping element between a shank releasing position and a shank clamping position, and is accommodated in an axial through-hole formed in the spindle. The actuating element of the tool retaining mechanism is driven by a drive mechanism (e.g., a hydraulic cylinder mechanism) provided outside the spindle head device, and acts to displace the movable clamping element in accordance with the axial displacement of the actuating element in the through-hole of the spindle.
In the machine tool as described above, the configuration of the shank of the tool holder and the corresponding configuration of the spindle nose of the spindle are standardized by standards such as JIS (Japan Industrial Standard), DIN (Deutsche Industrie Normen), JBS (Japan Bench Machine Tool Builders Association Standard), etc. For example, a tool shank standardized by JIS or JBS is configured to have an outer surface in the shape of a circular truncated cone (with 7/24 taper) and be provided with a rod-like element, referred to as a pull stud, fixed at the distal end of the tool shank, while a corresponding spindle nose is provided with a shank receiving recess having an inner surface in the shape of a circular truncated cone (with 7/24 taper) (JIS B6101, B6339; JBS 4001, 4002, etc.). On the other hand, a tool shank standardized by DIN is configured to be provided with a thin-wall, hollow tubular body having an outer surface in the shape of a circular truncated cone (with 1/10 taper), while a corresponding spindle nose is provided with a shank receiving recess having an inner surface in the shape of a circular truncated cone (with 1/10 taper) (DIN 69063-5, 69893-5, etc.).
A tool retaining mechanism for retaining a tool holder complying with JIS (JBS) on a spindle nose, is configured to clamp the pull stud at the distal end of the tool shank received in the shank receiving recess by a plurality of movable clamping elements provided to be disposed around the pull stud, in which the movable clamping elements are moved in a radial direction under the operation of the actuating element and thus are engaged with a shoulder surface of the pull stud from the outside thereof. In contrast, a tool retaining mechanism for retaining a tool holder complying with DIN on a spindle nose, is configured to clamp the tool shank received in the shank receiving recess by a plurality of movable clamping elements provided to be inserted into the hollow interior portion of the tool shank, in which the movable clamping elements are moved in a radial direction under the operation of the actuating element and thus are engaged with a shoulder surface of the tool shank from the inside thereof. In this connection, the configurations of the tool holder, the spindle nose and the tool retaining mechanism, complying with JIS (JBS), are described in, for example, Japanese Unexamined Patent Publication (Kokai) No. 9-314404 (JP-A-9-314404). The configurations of the tool holder, the spindle nose and the tool retaining mechanism, complying with DIN, are also described in, for example, Japanese Unexamined Patent Publication (Kokai) No. 5-220607 (JP-A-5-220607).
As described above, for a conventional machine tool provided with a tool spindle, there are several standards different in terms of mechanical structures and incompatible with each other, regarding the configurations of a tool holder, a spindle nose and a tool retaining mechanism. Thus, when a user of a machine tool intends to use different types of tool holders complying with incompatible standards, it is necessary for the user to prepare different types of machine tools provided respectively with spindle head devices for exclusive use, each spindle head device including a spindle and a tool retaining mechanism, complying with each standard. The user generally tends to store various types of tools in a state where they are attached to tool holders, so that in a case where, for example, the user intends to suitably select and use the mechanical configurations respectively complying with JIS and DIN while considering several requirements such as a machining precision, a tool life, an operating noise, etc., it is also necessary to permanently prepare machine tools respectively complying with JIS and DIN, even for the same type of tools. Therefore, in this case, equipment cost may increase, and maintenance and management may be complicated.
A conventional machine tool provided with a tool spindle is also configured such that, in each standard, a shank of a tool holder is received and retained in a shank receiving recess at a spindle nose. Therefore, repeated tool-changing works may cause a wear of the shank receiving recess of the spindle nose, and in such a case, the spindle needs to be replaced with new one. In this connection, the spindle is usually required to be machined in high precision at the inner surface thereof including the shank receiving recess and the outer surface thereof adapted to be fitted into a bearing unit, and in recent years, there is an increasing requirement of forming a fluid passage for supplying cleaning fluid or cooling fluid so as to penetrate through the spindle, so that the spindle has now become relatively expensive among all components of a machine tool. Therefore, if the tool-changing is frequently carried out, the replacement of such an expensive spindle with new one may result higher maintenance costs.